Flyback converter
View Patent ↗A flyback converter detects an output voltage at the primary coil without using a photo coupler and provides an essentially constant output voltage independent of the load size, thereby minimizing the number of additional coils used in the transformer circuit to realize simple construction and providing accurate power control. In one embodiment, the flyback converter includes: a transformer for changing an input voltage to a predetermined level according to a winding ratio; an output unit for rectifying the voltage signal output from the transformer into a DC signal to drive a load; a switch coupled to the primary coil of the transformer for controlling the on/off state of a power at the primary coil according to a switching control signal; a feedback unit generating a feedback signal and detecting a current of the switch to correct the feedback signal; and a switching controller operating according to the feedback signal.
1. A flyback converter, which provides an essentially constant output voltage independent of the size of a load, the flyback converter comprising:
a transformer operable to change an input voltage to a predetermined level according to a winding ratio of a primary coil to a secondary coil;
an output unit, coupled to the transformer, operable to rectify a voltage signal output from the transformer into a DC signal operable to drive the load;
a switch, coupled to the primary coil of the transformer, operable to control an on/off state of a power at the primary coil according to an input switching control signal;
a feedback unit, coupled to the transformer, operable to detect the voltage signal output by the transformer to the output unit, generating a feedback signal, detecting a switching current of the switch to correct the feedback signal, and outputting the corrected feedback signal, the feedback unit comprising:
a detecting coil operable to detect the power output from the transformer;
a driving power generator operable to rectify a detected signal of the detecting coil to generate a driving power for the operation of the switching controller;
a switch current operator operable to detect a current variation according to the switching operation of the switch to generate a converted current signal;
a gain regulator operable to regulate the gain of the converted current signal output from the switch current operator to generate a corrected current signal; and
a feedback signal generator operable to reduce the driving power signal output from the driving power generator by a voltage drop corresponding to the corrected current signal output from the gain regulator to generate a feedback voltage signal to the switching controller; and
a switching controller, coupled to the feedback unit and to the switch, operable to receive an output signal of the feedback unit and generating a switching control signal, operable to control the operation of the switch.
2. The flyback converter as claimed in claim 1 , wherein the driving power generator comprises:
a diode having an anode coupled to a terminal of the detecting coil;
a resistor having one terminal coupled to the cathode of the diode;
a capacitor having one terminal coupled to the other terminal of the resistor and the other terminal coupled to ground; and
a current source coupled between the both terminals of the capacitor.
3. The flyback converter as claimed in claim 2 , wherein the current source includes an operating current value of the switching controller or an additional current source.
4. The flyback converter as claimed in claim 1 , wherein the feedback signal generator comprises:
a resistor having one terminal coupled to an output signal of the driving power generator and the other terminal coupled to the gain regulator; and
a capacitor having one terminal coupled to the other terminal of the resistor and the other terminal coupled to ground.
5. A flyback converter, which provides a constant output voltage independent of the size of a load, the flyback converter comprising:
a transformer operable to change an input voltage to a predetermined level according to a winding ratio of a primary coil to a secondary coil;
an output unit operable to rectify a voltage signal output from the transformer into a DC signal and driving the load;
a switch coupled to the primary coil of the transformer operable to control the on/off state of a power at the primary coil according to an input switching control signal;
a feedback unit operable to detect the voltage signal output from the transformer to the output unit to generate a driving power, filtering the driving signal in multiple steps to generate a stabilized feedback signal, and detecting a switching current of the switch to correct the feedback signal, the feedback unit comprising:
a detecting coil operable to detect the power output from the transformer;
a driving power generator operable to rectify a detected signal of the detecting coil to generate a driving power for the operation of the switching controller;
a switch current operator operable to detect a current variation according to the switching operation of the switch to generate a converted current signal;
a gain regulator operable to regulate the gain of the converted current signal output from the switch current operator to generate a corrected current signal; and
a feedback signal generator operable to stabilize the driving power signal output from the driving power generator and reducing the stabilized driving power signal by a voltage drop corresponding to the corrected current signal output from the gain regulator to generate a feedback voltage signal to the switching controller; and
a switching controller operating according to the driving power output from the feedback unit to receive an output signal of the feedback unit and generate a switching control signal operable to control the operation of the switch.
6. The flyback converter as claimed in claim 5 , wherein the driving power generator comprises:
a diode having an anode coupled to a terminal of the detecting coil;
a resistor having one terminal coupled to the cathode of the diode;
a capacitor having one terminal coupled to the other terminal of the resistor and the other terminal coupled to ground; and
a current source coupled between both terminals of the capacitor.
7. The flyback converter as claimed in claim 5 , wherein the current source includes an operating current value of the switching controller or an additional current source.
8. The flyback converter as claimed in claim 5 , wherein the feedback signal generator comprises:
a first stage stabilizer and m-th to n-th stage stabilizers coupled in series for stabilizing the output signal of the driving power generator.
9. The flyback converter as claimed in claim 8 , wherein the first stage stabilizer comprises:
a resistor having one terminal coupled to an output signal of the driving power generator and the other terminal coupled to the gain regulator; and
a capacitor having one terminal coupled to the other terminal of the resistor and the other terminal coupled to ground.
10. The flyback converter as claimed in claim 5 , wherein the driving power generator comprises:
a diode having an anode coupled to a terminal of the detecting coil;
a capacitor having one terminal coupled to the cathode of the diode and the other terminal coupled to ground; and
a current source coupled between the both terminals of the capacitor.
11. The flyback converter as claimed in claim 10 , wherein the current source includes an operating current value of the switching controller or an additional current source.
12. The flyback converter as claimed in claim 5 , wherein the feedback signal generator comprises:
a first stage stabilizer and m-th to n-th stage stabilizers coupled in series for filtering the output signal of the driving power generator; and
a current source coupled to the after-terminal of any one of the stage stabilizers.
13. The flyback converter as claimed in claim 12 , wherein the current source includes an operating current value of the switching controller or an additional current source.
14. A flyback converter, which provides an essentially constant output voltage independent of the size of a load, the flyback converter comprising:
a transformer operable to change an input voltage to a predetermined level according to a winding ratio of a primary coil to a secondary coil;
an output unit, coupled to the transformer, operable to rectify a voltage signal output from the transformer into a DC signal operable to drive the load;
a switch, coupled to the primary coil of the transformer, operable to control an on/off state of a power at the primary coil according to an input switching control signal;
a feedback unit, coupled to the transformer, operable to detect the voltage signal output by the transformer to the output unit, generating a feedback signal, detecting a switching current of the switch to correct the feedback signal, and outputting the corrected feedback signal, the feedback unit not containing a photocoupler; and
a switching controller, coupled to the feedback unit and to the switch, operable to receive an output signal of the feedback unit and generating a switching control signal, operable to control the operation of the switch.
15. A flyback converter, which provides an essentially constant output voltage independent of the size of a load, the flyback converter comprising:
a transformer operable to change an input voltage to a predetermined level according to a winding ratio of a primary coil to a secondary coil;
an output unit, coupled to the transformer, operable to rectify a voltage signal output from the transformer into a DC signal operable to drive the load;
a switch, coupled to the primary coil of the transformer, operable to control an on/off state of a power at the primary coil according to an input switching control signal;
a single feedback unit, coupled to the transformer, operable to detect the voltage signal output by the transformer to the output unit, generating a feedback signal, detecting a switching current of the switch to correct the feedback signal, and outputting the corrected feedback signal, the feedback unit not connected to the secondary coil and the output unit; and
a switching controller, coupled to the feedback unit and to the switch, operable to receive an output signal of the feedback unit and generating a switching control signal, operable to control the operation of the switch.